1. Field of the Invention
This invention relates to devices for testing cables and, more particularly, relates to devices for automatically testing the continuity of center conductors and shields of a cable and for short circuits therebetween.
2. Description of Related Art
Conductors, such as cables and the like need to be checked for damage which is often not apparent to the naked eye. Typically, this is done by electrically testing a cable for continuity and short circuits. However, many known testing techniques are time consuming and tedious. Known techniques include, for example, manually probing the center conductor and shield of the cable. Although some cable testers indicate a fault in the cable, many do not distinguish between an open circuit in the center conductor and one in the shield. Other cable testers require the use of switches to determine whether the conductor or shield is faulty.
These known testing techniques are problematic because they are subject to human error. In addition, they can be very tedious especially when a vast number of cables have to be tested.
U.S. Pat. No. 4,670,709 to Iredale discloses a battery-powered audio cable test device which can test several different types of audio cable for shorts or opens when operated in a cable continuity mode. This device does not test center conductors and shields for continuity. Additionally, even when three prong cables are tested, the device does not specify which conductor is faulty, only that the cable is faulty.
U.S. Pat. No. 4,491,781 to McClintic discloses a battery-powered tester unit for determining if a short or a break exists in either of two conductive paths in a cable. The tester includes a pair of jacks adapted to receive plugs of a cable and a pair of indicating LEDs. Each of two contacts of the first jack is connected in series with an LED, the battery and the corresponding contact of the second jack so as to create a circuit that tests continuity in both of the conductors in a cable with both of its plugs connected to the tester. This device requires that a cable be tested separately for short circuits, and then for continuity. Accordingly, excessive time may be required to fully test a cable. Additionally, it is easy to forget to perform one of the two tests, especially when many cables are being tested.
U.S. Pat. No. 4,281,283 to Ross et al. discloses a portable battery-powered audio cable tester having two jacks for connecting a cable to be tested. A signal light and a push-button "short" switch are connected with a battery such that the light will switch on when a cable not having a "short" is connected to the tester and off when the short switch is opened, indicating the absence of a short. However, a position toggle switch must be actuated along with the push button "short" switch to distinguish between malfunctions due to a broken conductor, an open shield, or a short circuit.
U.S. Pat. No. 4,553,085 to Canzano discloses a coaxial cable tester device having a transmitter unit and a receiver unit, each with two coaxial connectors. The cable tester device determines whether a cable is defective, whether the defect is an open circuit or a short circuit and in which cable conductor the defect occurs. This system is bulky and also requires the manipulation of a switch and multiple cable connection sequences in order to test for conductor and shield continuity, and for a short circuit.